Fuel depletion alarm circuit utilizing bimetal



Dec. 9, 1969" E. w. KRAFT ET AL 3,483,500

FUEL DEPLETION ALARM CIRCUIT UTILIZING BIMETAL Original Filed Nov. 12, 1964 Frank C. Weaver a, a i

A -//arney United States Patent 3,483,500 FUEL DEPLETION ALARM CIRCUIT UTILIZING BIMETAL Edmond W. Kraft, Roselle, and Frank C. Weaver,

Chicago, Ill., assignors to Stewart-Warner Corporation, Chicago, Ill., a corporation of Virginia Original application Nov. 12, 1964, Ser. No. 410,689. Divided and this application June 4, 1968, Ser. No.

Int. Cl. H01h 61/013, 71/16 US. Cl. 337-104 1 Claim ABSTRACT OF THE DISCLOSURE An E-shaped bimetal switch structure secured at the center leg to a support with the back leg having a transverse rib and the side legs having switch contacts.

BACKGROUND OF THE INVENTION Field of the invention The present application is a division of Patent Application Ser. No. 410,689, filed Nov. 12, 1964, now Patent No. 3,403,376, and relates to a circuit assembly employing bimetal switching elements for indicating an alarm condition such as occurs on fuel depletion in a motor vehicle.

Description of the prior art Bimetal type switches are usually employed with 12 volt automobile ignition and lamp systems for transmitting a constant voltage of 5 or 6 volts to various bimetal gauges. The bimetal gauges are utilized for indicating,

' for example, fuel volume, oil pressure, or temperature and/ or other conditions. Although the bimetal fuel gauge,

for example, may indicate fuel depletion to be a low level, it is desirable to call the operators attention to his gauge, since he may neglect to look at same. For this purpose it is necessary to employ some lighting or alarm system for alerting the operator so that he will examine his gauge and note the fuel situation.

Since the lighting system will conventionally employ the full battery voltage while the bimetal gauge operates from the 5 or 6 volt constant voltage supply, a problem arises in operating both the bimetal gauge and a lamp under control of the same sensing element which detects the fuel level.

SUMMARY OF THE INVENTION It is, therefore, one object of the present invention to provide an improved automotive alarm system for signal ing a fuel depletion condition through a 12 volt lamp from a sensing source adapted to simultaneously control a bimetal gauge operating on substantially 5 volts.

It is another object of the present invention to provide an improved and more reliable arrangement for operating an alarm signal responsive to a fuel depletion condition in an automobile whereby either of two different indicators may be independently operated to signal said condition.

It is yet another object of the present invention to employ a 12 volt alarm system for indicating fuel depletion conditions in an automobile without altering the conventional parameters of a 5 volt bimetal gauge or the sender associated therewith.

It is also an object of the present invention to introduce a simple and economical arrangement for delaying the operation of a fuel depletion alarm system to ensure that the depletion actually exists.

It is still a further object of the present invention to provide an improved bimetal construction for enabling a 3,483,500 Patented Dec. 9, 1969 plurality of bimetal switches to be operated on a single bimetal structure.

Other objects and features of the present invention will become apparent upon examination of the following specification and claim together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a circuit arrangement incorporating the principles of the present invention together with a perspective view of a plurality of bimetal switches arranged on a unitary bimetal structure; and

FIG. 2 is a sectional view taken through the line 2-2 in FIG. 1.

In FIG. 1 a circuit for accomplishing the purposes of the present invention is indicated generally by the reference character 10 with a unique bimetal assembly for use with the circuit 10 indicated by character 12. The circuit 10 includes a conventional nominal 12 volt battery indicated at B and normally supplying as much as 14 volts. The output of battery B is passed through an ignition switch indicated at I to one terminal of a lamp 14; to a terminal 16 on the assembly 12 and also to a set of normally closed contacts 18 of a conventional bimetal constant voltage switch 20. The switch 20 has a coil 22 which is energized through contacts 18 and the bimetal for periodically Opening the contacts 18 to thereby supply a substantially constant 5 volts through the contacts 18 to terminal 23 on assembly 12 and over lead 24 to one or more conventional bimetal gauges such as fuel gauge 25.

The bimetal fuel gauge 25 indicates a coil 26 having one terminal connected to contacts 18 over lead 23 and the other terminal connected to one end of a sender or rheostat 28. The other end of rheostat 28 is connected to a terminal 30 on assembly 12. The rheostat has an arm 32 connected to ground, and the arm 32 varies the resistance of the rheo-stat with respect to coil 26 in response to the movement of the conventional float arm in the fuel tank as the fuel level varies. The resistance values of the rheostat and coil 26 may thus be maintained at their conventional values irrespective of the potential at terminal 30 for controlling the indicating pointer 33 of the fuel gauge in accordance with the fuel level.

The assembly 12 includes terminals 34, 36 and 38 in addition to terminals 14, 16 and 30, all mounted on an electrically insulating card 40. Terminals 23 and 16 are connected to one end of a respective coil 42 and 44, 1

while terminals 30 and 34 are connected to the other end of coils 42 and 44 respectively. Terminal 36 is connected to the other terminal of lamp 14, and terminal 38 is connected to ground through a metal foil 39. The resistance of coils 42 and 44 is in the order 35 ohms and 235 ohms respectively, and each is mounted on a respective end leg 46 and 48 of an E-shaped bimetal lamination or structure 50. Terminal 38, which is an L-shaped grounding strip eyeleted or riveted to card 40, has one end welded to structure 50. The foil 39 is sandwiched between card 40, and strip 38 projects beyond the end of the card to establish a ground connection to a cover 51 which is assembled to the card and easily folds the foil into a clamped secure position.

The structure 50 includes a center leg 52 and all three legs 46, 48 and 51 are interconnected by a back leg 53 having a transverse rib section 54. Practical dimensions for legs 46, 48 and 52, excluding normal tolerances, are .1" wide for leg 46, .290" wide for leg 48, and A for leg 52. The bimetal structure 50 is approximately .02" thick with the space between legs 46 and 52 in the order of .290" and that between legs 48 and 52 being A". The length of the legs 46, 48 and 52 to leg 53 is in the neighborhood of 1.15", and the width of back leg 53 is sub- 3 stantially .06". The height of section 54 is approximately .07". Thus the two side legs 46 and 48, together with the back leg 53 are supported cantilever fashion from the strip 38 and float above the card.

A contact 56 is provided at the end of legs 46 and 48 respectively, opposite back leg 52. Each contact 56 is adapted to engage a respective contact 58 only after the respective leg 46 or 48 has been heated to a desired degree. The contacts 58 are suspended on the end of respective flexible arms 60. The arms 60 are fixed to terminals 34 and 36 respectively. Adjustment of the contact spacing is effected by energizing the coils to a desired degree and threading a screw member 62 through the card 36 against contact 58 to ensure that the contacts close at the proper time, and cementing the screws, when the adjustment is complete.

Thus coil 42 is adapted to be energized to a degree dependent on the position of arm 32 of rheostat 28 which in turn is controlled by the fuel tank float. Coil 26 is thus enabled to operate from its conventional 5 volt constant voltage supply without altering its parameters, while a failure developing in the circuit to either coil 42 or 26 does not incapacitate the other coil. If desired, coil 42 may be operated from the 12 volt supply while connected to rheostat 28 as shown without altering the parameters of coil 26; however, this would require a larger number of turns on coil 42.

The leg 46 will respond to the current passing through coil 42 by flexing about its juncture with leg 53. Stability of leg 53 with regard to flexure about an axis perpendicular thereto is ensured by the transverse rib section 54. Thus leg 46 flexes downward to a degree dependent on the voltage drop across coil 42. When the fuel level is sufliciently low, preferably about 3 gallons, coil 42 is energized sufficiently to cause the associated contacts 56 to engage contact 58.

A circuit from the 12 volt supply extended through terminal 16 and coil 44 is therefore completed through terminal 34 and bimetal legs 46 and 52 to ground through terminal 38. The coil 44 therefore energizes to initiate flexing of the bimetal leg 48 about its juncture with leg 53. After a desired period of time contact 56 on leg 48 engages adjacent contact 58 to extend a circuit from battery through the alarm lamp 14 and terminal 36 to ground over the bimetal legs 48 and 52 and terminal 38. The

alarm lamp 14 now lights to signal that the fuel level has fallen below a desired level.

It will be noted that the lamp 14 is operated under control of coil 44 to introduce a desired time delay and not under direct control of coil 42. The reason for this is that there are occasions when the fuel level in the tank is temporarily distributed as may occur when the vehicle is rounding curves or corners. Under these circumstances the float may cause coil 42 to energize sufiiciently to operate its contacts. However, since the lamp 14 does not light until coil 44 has closed its associated contacts 56 and 58, temporary. dislocations in the fuel level do not cause unnecessary alarms. The choice of operating the lamp and coil 44 from the 12 volt supply instead of the 5 volt supply is in good part dictated by the need to avoid overloading the 5 volt circuit and the availability of the 12 volt supply.

In brief, therefore, the bimetal switch 20 supplies a constant voltage to a series of coils such as 26 at various bimetal gauges. The coil 26 operates the associated pointer to indicate the fuel level in correspondence with the position of arm 32 at rheostat 28. If the fuel level is above a predetermined value, for example, 3 gallons, coil 42 does not close the associated contacts 56 and 58 although it is energized. If the fuel level falls below the predetermined value, coil 42 is energized sufiiciently to close its associatd contacts 56 and 58 to energizecoil 44.

After a period of time, sufficient to ensure that coil 44 has been energized as a result of a true low level fuel condition, coil 44 closes its associated contacts to energize lamp 14 and alert the operator of the low fuel condition, whereafter appropriate steps may be taken. Thus coil 42 must be energized to a predetermined degree before it energizes coil 44, and coil 44 in turn must be energized for a predetermined time period before the lamp 14 is lighted.

The foregoing constitutes a description of an improved bimetal switch structure having inventive concepts believed to be set forth in the following claim.

What is claimed is:

1. A bimetal switch comprising an E-shaped bimetal lamination substantially .02" thick with all longitudinal edges of the side and center legs being parallel and the center leg having a width of substantially A and intermediate the respective side leg widths one of which is substantially less than Mr" wide and the other of which is substantially greater than A" wide, a coil on opposite side legs of said lamination, a contact on the end of each side leg opposite the back leg, another contact for each side leg contact for engagement with a respective side leg contact in response to a predetermined degree of energization of the respective coil for flexing the respective side leg about a respective position spaced from the respective end contact, a transverse rib section on said back leg, a card of electrically nonconducting material carrying each other contact, means on said card for extending an electrical connection to each coil, means fixing the end of said center leg opposite said back leg to said card for enabling automatic adjustment of the respective position of flexure of each side leg to compensate for changes in ambient temperature, an electrically conducting cover engaging said card for enclosing said bimetal lamination on said card, and means fixed to said center leg end and said card for extending an electrical connection between said center leg and said cover on engagement of said cover with said terminal board.

References Cited UNITED STATES PATENTS 7 2,255,672 9/1941 Mason 337-103 2,819,365 1/1958 Epstein 337-111 3,010,097 11/1966 Body 337-103 3,234,346 2/1966 Taylor et a1 337-111 BERNARD A. GILHEANY, Primary Examiner R. L. COHRS, Assistant Examiner U.S. Cl. X.R. 337-103, 111 

